What Is a Current Meter?
A current meter is a measuring instrument used to determine the velocity of water flowing in a river or air being discharged from a duct.
Current meter products are developed based on various measurement principles, such as the rotational speed of an impeller or the Doppler effect of ultrasonic waves. While current meters and flowmeters are similar, measuring flow velocity and flow rate, they are generally treated as the same type of measuring instrument.
Uses of Current Meter
Current meters are used in diverse applications, from river and dam surveys to industrial production plants. They are employed to measure river flow velocity, and exhaust gas velocity, control the inflow velocity in plastic injection molding, and manage the inflow of chemical solutions.
When selecting a current meter, considerations include the range of velocities to be measured, durability, maintenance ease, and whether it is a non-contact or contact type. Many models incorporate communication devices for remote monitoring, enhancing work efficiency.
Principles of Current Meter
Current meters are based on two main principles: electric current meters using an impeller and ultrasonic current meters using ultrasonic waves. They typically comprise a measuring section, an information processing device for electrical signals, and a communication device.
1. Electric Type
Electric current meters measure flow velocity by the number of impeller revolutions. A magnet attached to the impeller generates a magnetic field change, which is converted into an electrical signal and transmitted as a pulse to the information processing unit.
The impeller is aligned with the fluid flow direction using weights or similar devices.
2. Ultrasonic Type
Ultrasonic current meters emit ultrasonic waves towards the fluid, measuring the flow velocity based on the phase shift of waves bouncing off the water surface. This non-contact measurement method enables safe, remote monitoring without disturbing the fluid flow.
Types of Current Meter
Beyond electric and ultrasonic types, current meters come in various forms:
1. Differential Pressure Type
The differential pressure type uses an orifice in the fluid path, measuring flow velocity from the pressure difference across the orifice. It is used for gases, liquids, and vapors and is cost-effective, with no moving parts, making it easy to maintain.
2. Electromagnetic Type
Electromagnetic flowmeters apply Faraday’s law of electromagnetic induction. A magnetic field generated at a 90-degree angle to the flow of a conductive fluid induces an electromotive force proportional to the flow velocity. This method is suitable for conductive fluids and is unaffected by liquid properties like temperature, pressure, density, or viscosity.
3. Coriolis Method
The Coriolis current meter uses the Coriolis force, an apparent force in a rotating system, to measure flow. The faster the fluid flows, the greater the Coriolis force and resulting pipe deformation.
4. Thermal Type
The thermal type measures flow velocity based on the heat absorption of a fluid from a heat source. The flow velocity is determined by the temperature difference at two points in the fluid path or the power consumption of a controlled heater that maintains a consistent temperature difference.
5. The Kalman Vortex Method
This method calculates flow velocity by detecting Kalman vortices, which form downstream of a columnar obstacle in the fluid. Some models use piezoelectric elements to detect vortex vibrations, while others employ ultrasonic detection.